There are many types of serial communications protocols known in the art. One such communications protocol is MODBUS. MODBUS is a serial communications protocol first published in 1979 for use with its programmable logic controllers (PLCs). It has become a de facto standard communications protocol in industry, and is now the most commonly available means of connecting industrial electronic devices. More particularly, the MOSBUS protocol is often used for sending information between a client and server of a MODBUS enabled system. There are many types of MODBUS enabled systems known in the art, such as the MODBUS enabled system 100 shown in FIG. 1A.
System 100 is configured for controlling industrial equipment and processes. The system 100 is typically comprised of a first industrial control system (FICS) 102, a gateway node 120, a second industrial control system (SICS) 122, and industrial equipment 118, 126. The FICS and SICS 102, 122 can have a distributed network configuration, i.e., there are application specific modules connected to each other, industrial equipment 118, 126, and operator interfaces via a local control network. The gateway node 120 is configured to enable communications between the FICS 102 and SICS 122.
As shown in FIG. 1A, the FICS 102 generally includes a serial bus 104 having a particular data transfer rate (e.g. 9,600 bits per second (BPS)) and MODBUS server devices 106, 108, 110, 112 connected to and accessible by other portions of the system 100 through the serial bus 104. Each of the MODBUS server devices 106, 108, 110, 112 is comprised of a memory device 130, 132, 134, 136 including respective storage locations 1401, . . . , 140N, 1421, . . . , 142N, 1441, . . . , 144N, 1461, . . . , 146N. Each of the memory devices 130, 132, 134, 136 has process parameter information stored therein. Such process parameter information generally includes, but is not limited to, information defining temperature parameters, timing parameters, and liquid level parameters.
SICS 122 is comprised of a computing system (or MODBUS client device) 124. The computing system 124 is typically a desktop personal computer system, a laptop personal computer system, a personal digital assistant, a wireless computing device, or any other general purpose computer processing device. The computing system 124 is configured to allow users to monitor and/or control an industrial process or equipment 126. More particularly, the computing system 124 is configured to enable a user to write parameter information to and/or read parameter information from each of the MODBUS server devices 106, 108, 110, 112.
A typical write process is shown in FIG. 1B performed by the MODBUS enabled system 100 of FIG. 1A. The write process generally involves generating a write request at the computing device 124 and sending the write request from the computing device 124 to the gateway node 120. The write request comprises data to be written to one or all of the memory locations of the MODBUS server device. Upon receipt of the write request, the gateway node 120 transitions out of an IDLE state, generates a write request message and sends the write request message to a MODBUS server device (e.g., MODBUS server device 108). The phrase “IDLE state” as used herein refers to a condition that exists whenever there are no outstanding write/read requests and transaction resources are immediately available for use. The write request message includes an entire data block (i.e., N bits or bytes) or a portion of a data block (i.e., a single bit or byte). After receiving the write request message the MODBUS server device performs write operation for writing data to one or all of the memory locations (e.g., 1421, . . . , 142N) in the MODBUS server device. The MODBUS server device also generates a response message and communicates the same to the gateway node 120. The gateway node 120 forwards the response message to the computing device 124. Thereafter, the gateway node 120 transitions into its IDLE state so that transaction resources are freed.
A typical read process is shown in FIG. 1C performed by the MODBUS enabled system 100 of FIG. 1A. The read process generally involves generating a reading query at the computing device 124 and sending the reading query from the computing device 124 to the gateway node 120. Upon receipt of the reading query, the gateway node 120 transitions out of an IDLE state, generates a read request message, and sends the read request message to a MODBUS server device (e.g., MODBUS server device 108). After receiving the read request, the MODBUS server device performs read operations, generates a response message, and communicates the response message to the gateway node 120. The gateway node 120 forwards the response message to the computing device 124. The response message includes an entire data block (i.e., N bits or N bytes). Thereafter, the gateway node 120 transitions into its IDLE state so that transaction resources are freed.
Despite the advantages of conventional MODBUS enabled system 100, system 100 suffers from certain drawbacks. For example, the communications between the serial MODBUS devices 124, 120, 106, 108, 110, 112 are restricted by the bandwidth of the serial bus 104, which is typically 9,600 bps. In addition, the read/write processes are restricted to a single read or write request at any given time. Accordingly, the rate of transferring data to the serial MODBUS devices 124, 120, 106, 108, 110, 112 is severely limited. As such, there is a need for an improved serial communication protocol (SCP) enabled system capable of transferring data to the SCP devices at a higher rate as compared to conventional SCP enabled systems.